The present invention relates to a pneumatic nailing machine having a mechanism for regulating a driving depth of nails or other fasteners into a workpiece.
It is desirable that the driving depth at which a pneumatic nailing machine drives nails into a workpiece be adjustable. When nails are driven into the workpiece too deeply, the surface of the workpiece around the nail head can be indented by the nail head, resulting in a pitted and uneven workpiece surface. On the other hand, if the driving depth is insufficient, the nail head is projected or separated from the top surface of the workpiece.
Japanese Utility Model Application Kokai No. HEI-3-52083 describes such a conventional pneumatic nailing machine wherein the driving depth is adjustable. As shown in FIG. 1, the conventional pneumatic nailing machine 101 has a body 102 with a nose portion 108. A trigger 112 is pivotally movably provided to the body 102, and an operation lever 142 is pivotally movably provided to the trigger 112. A trigger valve 110 is provided for providing a pneumatic force to a piston 106, and a plunger 111 is provided to actuate the trigger valve 110. If the operation lever 142 is pivotally moved to a pivot position, the operation lever 142 can be abuttable on the plunger 111, so that the trigger valve 110 is actuated upon manipulation to the trigger 112. On the other hand, if the operation lever 142 is in a rest position, the operation lever 142 does not abut the plunger 111 even by the manipulation to the trigger 112. The pivotal movement of the operation lever 142 is provided by a vertical movement of a support shaft 140.
A push lever 114 is provided attached to the nose 108 of the body 102. As shown in FIGS. 2 through 4, the push lever 114 has two sections: a first push lever 128 and a substantially L-shaped second push lever 129 connected to the support shaft 140. A bearing collar 132 is provided to the second push lever 129. An elliptical hole 123 formed elongated in the direction horizontal to the vertically elongated shape of the push lever 114 is provided opened in the first push lever 128.
A connection unit 131 is provided for slidably connecting the first push lever 128 to the second push lever 129. The connection unit 131 includes an adjustment mechanism 117 and a support unit 130. The adjustment mechanism 117 includes an adjustment shaft 118 that is rotatably supported engaged in the bearing collar 132. A flange 119 is provided on the end of the adjustment shaft 118 that faces the nose 108. A knob 120 for rotating the adjustment shaft 118 is provided to the opposite end of the adjustment shaft 118. The adjustment mechanism 117 also includes an eccentric body 121 provided fixed around the lengthwise center of the adjustment shaft 118, between the knob 120 and the bearing collar 132, so as to rotate in association with the rotation of the adjustment shaft 118. The eccentric body 121 is also engaged in the elliptical hole 123 of the first push lever 128. With this configuration, rotation of the eccentric body 121 moves the first push lever 128 vertically in relation to the second push lever 129.
The support unit 130 ensures vertical orientation of the first push lever 128 even by the eccentric rotation of the eccentric body 121. That is, the first push lever 128 is formed with a first slot 128a and a second slot 128b, and the support unit 130 includes a screw 150 fixedly secured to the second push lever 129 and extending through the first slot 128a, and a protrusion 151 extending from the second push lever 129 into the second slot 128b. Accordingly, vertical movement of the first push lever 128 by the rotation of the eccentric body 121 is guided by the sliding engagement between the screw 150 and the first slot 128a and between the protrusion 151 and the second slot 128b.
The operation lever 142 for preventing or allowing the trigger 112 to be pulled is pivotally provided in a trigger 112. A guide member 141 with a vertically running cylindrical bore opened therein is provided to the body 102 beneath the trigger 112. The support shaft 140 is supported in the bore of the guide member 141 so as to be vertically slidable therein.
A screw 160 for fixing the push lever 114 to the support shaft 140 is fixed to the tip of the vertical arm of the substantially L-shaped second push lever 129. With this configuration the support shaft 140 protrudes from the guide member 141 and abuts the free tip of the operation lever 142 when the push lever 114 is moved upwardly, that is, when the lower end 115 of the first push lever 128 is forcibly pressed against the workpiece surface.
With this conventional mechanism for adjusting the driving depth, the distance at which the tip of a driving rod 105 protrudes from the pneumatic nailing machine is adjusted by adjusting the length of the push lever 114. The push lever 114 is elongated or shortened by rotating the adjustment mechanism 117 near the nose 108, thereby adjusting the distance between the tip of the push lever 115 and the tip surface 109 of the nose 108.
When the eccentric body 121 is in the posture shown in FIG. 2, the first push lever 128 is raised as high as allowed by the adjustment mechanism 117. The overall length of the push lever 114 is at a minimum, which results in nails being driven into the workpiece to the maximum possible depth. On the other hand, when the eccentric body 121 is in the posture shown in FIG. 4, the overall length of the push lever 114 is at a maximum, which results in nails being driven into the workpiece to the minimum possible depth because the distance between the nose tip surface 109 and the push lever tip surface 115 becomes the longest.
However there has been known a problem with this conventional adjustment arrangement in that because the adjustment mechanism 117 is located near the nose 108, an operator can not reach the adjustment mechanism 117 with the same hand that holds the handle 103 while holding the handle 103. The adjustment mechanism 117 can be operated by the other hand (i.e., the hand not holding the handle 103), but when the operator is holding the workpiece in place during nail driving operations, the operator must release the workpiece to adjust the adjustment mechanism 117. Therefore, the adjustment mechanism 117 can not be operated during operations wherein the workpiece must be held in place by hand.
Also, the adjustment mechanism 117 gets in the way during operations in confined areas, such as in corners because of its position near the nose 108. Additionally, the connection unit 131 is necessary because the push lever 114 is formed from the first push lever 128 and the separate second push lever 129. This increases the complexity of the device.
Further, the pneumatic nailing machine may be accidentally fired if the push lever 114 is accidentally pressed against a solid object while the trigger 112 is being pulled in a sequential nail driving operation. This is due to the fact that the trigger 112 is always manipulatable regardless of the nail driving operation. Therefore, if the push lever 114 is depressed to move the support shaft 140 upwardly, a nail is driven if the trigger is inadvertently manipulated.